The present invention relates to a laser oscillating apparatus for generating a laser beam by introducing an electromagnetic wave from a waveguide into a laser tube through a plurality of fine slots formed in the waveguide wall and, for example, to a laser oscillating apparatus using a microwave as an electromagnetic wave for exciting a laser gas, an exposure apparatus using the same, and a device fabrication method using the same.
Recently, a so-called excimer laser has attracted attention as the only high-output laser which oscillates in the ultraviolet region. This excimer laser is expected to be applied to the electronic, chemical, and energy industries, particularly processing and chemical reactions of metals, resins, glass, ceramics, and semiconductors.
The principle of function of an excimer laser oscillator will be described below. First, laser gases such as Ar, Kr, Ne, F2, He, Xe, and Cl2 contained in a laser tube are excited by electron beam irradiation or discharge. Excited F atoms bond to inert Kr and Ar atoms in the ground state to generate KrF+ and ArF+ as molecules existing only in an excited state. These molecules are called excimers. Since excimers are unstable, they immediately emit ultraviolet rays and fall to the ground state. This phenomenon is called spontaneous emission. An excimer laser oscillator uses this to amplify as an in-phase beam in an optical resonator constructed of a pair of reflecting mirrors and extract as a laser beam.
In the case of excimer laser emission, microwaves are mainly used as a laser gas exciting source. Microwaves are electromagnetic waves having an oscillation frequency of a few hundred MHz to several tens of GHz. In this case, a microwave is introduced from a waveguide into a laser tube through a slot formed in the waveguide wall, thereby exciting a laser gas in the laser tube into a plasma.
Even if the intensity distribution of microwaves emitted through the slots is uniform, a slot array structure in which a plurality of slots are arrayed in the long-axis direction of a resonator must be formed in order to supply a microwave to a long space meeting the resonator length of a laser beam. This structure is shown in FIG. 22. Referring to FIG. 22, a plurality of fine slots 302 are formed at equal intervals in a waveguide wall 301. For convenience, the interior of a laser tube is schematically shown as an emission space.
When this slot array structure is used, regions (hatched elliptic regions in FIG. 22) between adjacent slots 302 are necessarily microwave non-irradiation regions. Accordingly, when a laser gas existing in the emission space is to be excited by a microwave, the existence of these non-irradiation regions produces variations in the microwave intensity. This generates plasma discharge having a nonuniform distribution as a whole.
The present invention has been made in consideration of the above problem, and has as its object to realize, for example, almost uniform electromagnetic wave radiation as a whole over the length of a laser tube in a slot array structure, thereby allowing almost uniform laser emission with minimum energy loss.
A laser oscillating apparatus according to the first aspect of the present invention comprises a waveguide in which a plurality of slots are formed and a laser tube to excite a laser gas in the laser tube by supplying an electromagnetic wave from the waveguide into the laser tube through the slot and generate a laser beam by resonating light generated by excitation of the laser gas, wherein electromagnetic waves with in-phase electric fields are supplied to the laser tube through the plurality of slots.
In the laser oscillating apparatus according to the first aspect of the present invention, the plurality of slots may be formed in a long end face or short end face of the waveguide.
Preferably, in the laser oscillating apparatus, wherein the plurality of slots and the laser tube are spaced apart from each other by a predetermined distance, and the laser oscillating apparatus further comprises a passage for guiding electromagnetic waves from the plurality of slots to the laser tube. The distance between the plurality of slots and the laser tube is preferably an integral multiple of a half-wave length. It is preferable that the width of the passage be substantially equal to a width of the slot. Preferably, the width of the passage is an integral multiple of a half-wave length of an electromagnetic wave supplied from the wave guide to the laser tube. A portion through which the passage communicates with the laser tube preferably has one or a plurality of slit portions each having a predetermined width and extending over a length of the laser tube. For example, a portion through which the passage communicates with the waveguide preferably has a width larger than a width of a portion through which the passage communicates with the laser tube.
In the laser oscillating apparatus according to the first aspect of the present invention, the passage is preferably filled with a dielectric substance. The waveguide is preferably filled with a dielectric substance. The plurality of slots are filled with a dielectric substance. In this case, the plurality of slots are preferably filled with the dielectric substance such that a surface in which the plurality of slots are formed is flattened.
In the laser oscillating apparatus according to the first aspect of the present invention, the pair of waveguides are arranged to sandwich the laser tube.
The laser oscillating apparatus according to the first aspect of the present invention preferably further comprises, for example, an adjusting portion for adjusting an impedance of each of the plurality of slots. The adjusting portion preferably includes a minute metal member attached to the short end face of the waveguide.
According to the second aspect of the present invention, there is provided a laser oscillating apparatus which includes a waveguide in which a plurality of slots are formed and a laser tube to excite a laser gas in the laser tube by supplying an electromagnetic wave from the waveguide into the laser tube through the slot, and generate a laser beam by resonating light generated by excitation of the laser gas, wherein the plurality of slots are formed in a long end face of the waveguide, and the plurality of slots are arranged at a predetermined pitch along a central line in a longitudinal direction of the long end face to be alternately located on left and right sides of the central line and spaced apart from the central line by a predetermined distance.
In the laser oscillating apparatus according to the second aspect of the present invention, electromagnetic waves with in-phase electric fields are preferably supplied to the laser tube through the plurality of slots.
In the laser oscillating apparatus according to the second aspect of the present invention, the predetermined pitch is preferably determined such that electromagnetic waves with in-phase electric fields are supplied to the laser tube through the plurality of slots.
Preferably, in the laser oscillating apparatus according to the second aspect of the present invention, the plurality of slots and the laser tube are spaced apart from each other by a predetermined distance, and the laser oscillating apparatus further comprises a passage for guiding electromagnetic waves from the plurality of slots to the laser tube. The distance between the plurality of slots and the waveguide is preferably an integral multiple of a half-wave length. Preferably, the width of the passage is substantially equal to a width of the slot. The width of the passage is preferably an integral multiple of a half-wave length of an electromagnetic wave supplied from the waveguide to the laser tube. A portion through which the passage communicates with the laser tube preferably has, for example, one or a plurality of slit portions having a predetermined width and extending over a length of the laser tube. A portion through which the passage communicates with the waveguide preferably has a width larger than, for example, a width of a portion through which the passage communicates with the laser tube.
In the laser oscillating apparatus according to the second aspect of the present invention, the passage is preferably filled with a dielectric substance. The waveguide is preferably filled with a dielectric substance. The plurality of slots are preferably filled with a dielectric substance. The plurality of slots are preferably filled with the dielectric substance such that a surface in which the plurality of slots are formed is flattened.
In the laser oscillating apparatus according to the second aspect of the present invention, the pair of waveguides are preferably arranged to sandwich the laser tube.
Preferably, the laser oscillating apparatus according to the second aspect of the present invention further comprises an adjusting portion for adjusting an impedance of each of the plurality of slots. The adjusting portion preferably includes a minute metal member attached to the short end face of the waveguide.
According to the third aspect of the present invention, there is provided a laser oscillating apparatus for generating a laser beam by exciting a laser gas and resonating light generated by excitation of the laser gas, comprising a pair of waveguides in each of which a plurality of slots are formed, the pair of waveguides being arranged such that surfaces in each of which the plurality of slots are formed opposite to each other, and a laser tube placed between the pair of waveguides, wherein electromagnetic waves with in-phase electric fields are supplied to the laser tube through the plurality of slots formed in each of the pair of waveguides.
In the laser oscillating apparatus according to the third aspect of the present invention, the plurality of slots are preferably formed in a long end face of each of the pair of waveguides. The plurality of slots are preferably formed in two lines in each of the pair of waveguides.
In the laser oscillating apparatus according to the third aspect of the present invention, the plurality of slots are preferably formed in a short end face of each of the pair of waveguides. The plurality of slots are preferably formed in a line in each of the pair of waveguides.
In the laser oscillating apparatus according to the third aspect of the present invention, the plurality of slots formed in each of the pair of waveguides are preferably arranged such that electromagnetic waves with in-phase electric fields are supplied to the laser tube.
Preferably, in the laser oscillating apparatus according to the third aspect of the present invention, the plurality of slots are formed at a predetermined pitch in each of the pair of waveguides, a position of the plurality of slots formed in one waveguide in a longitudinal direction of the laser tube is shifted from a position of the plurality of slots formed in the other waveguide in the longitudinal direction of the laser tube by a predetermined distance.
Preferably, in the laser oscillating apparatus according to the third aspect of the present invention, the plurality of slots are formed at a predetermined pitch in, for example, each of the pair of waveguides, and the laser oscillating apparatus further comprises an electromagnetic wave supplying portion for supplying electromagnetic waves with a predetermined phase difference to each of the pair of waveguides.
Preferably, in the laser oscillating apparatus according to the third aspect of the present invention, the plurality of slots are formed at a predetermined pitch in each of the pair of waveguides, a position of the plurality of slots formed in one waveguide in a longitudinal direction of the laser tube is shifted from a position of the plurality of slots formed in the other waveguide in the longitudinal direction of the laser tube by a predetermined distance, and the laser oscillating apparatus further comprises an electromagnetic wave supply portion for supplying electromagnetic waves with a predetermined phase difference to each of the pair of waveguides, whereby electromagnetic waves with in-phase electric fields are supplied to the laser tube through the plurality of slots formed in each of the pair of waveguides.
Preferably, the laser oscillating apparatus according to the third aspect of the present invention further comprises a tuner for tuning electromagnetic waves to the pair of waveguides.
In the laser oscillating apparatuses according to the first to third aspects of the present invention, the electromagnetic wave supplied from the waveguide to the laser tube is preferably a microwave.
In the laser oscillating apparatuses according to the first to third aspects of the present invention, the laser gas is preferably one of at least one type of gas selected from the group consisting of Kr, Ar, and Ne, and a gas mixture of the one type of gas and F2 gas, and the laser oscillating apparatus preferably comprises an excimer laser oscillating apparatus.
According to the fourth aspect of the present invention, there is provided an exposure apparatus comprising a laser oscillating unit, an illumination optical system for generating illuminating light for irradiating a mask by using illuminating light supplied from the laser oscillating unit, and a projection optical system for projecting a pattern of the mask illuminated with the illuminating light generated by the optical system onto a substrate, wherein the laser oscillating unit includes a waveguide in which a plurality of slots are formed and a laser tube to excite a laser gas in the laser tube by supplying an electromagnetic wave from the waveguide into the laser tube through the slot, and generate a laser beam by resonating light generated by excitation of the laser gas, and electromagnetic waves with in-phase electric fields are supplied to the laser tube through the plurality of slots.
According to the fifth aspect of the present invention, there is provided an exposure apparatus comprising a laser oscillating unit, an illumination optical system for generating illuminating light for irradiating a mask by using illuminating light supplied from the laser oscillating unit, and a projection optical system for projecting a pattern of the mask illuminated with the illuminating light generated by the optical system onto a substrate, wherein the laser oscillating unit includes a waveguide in which a plurality of slots are formed and a laser tube to excite a laser gas in the laser tube by supplying an electromagnetic wave from the waveguide into the laser tube through the slot, and generate a laser beam by resonating light generated by excitation of the laser gas, the plurality of slots are formed in a long end face of the waveguide, and the plurality of slots are arranged at a predetermined pitch along a central line in a longitudinal direction of the long end face to be alternately located on left and right sides of the central line and spaced apart the central line by a predetermined distance.
According to the sixth aspect of the present invention, there is provided an exposure apparatus comprising a laser oscillating unit, an illumination optical system for generating illuminating light for irradiating a mask by using illuminating light supplied from the laser oscillating unit, and a projection optical system for projecting a pattern of the mask illuminated with the illuminating light generated by the optical system onto a substrate, wherein the laser oscillating unit excites a laser gas and generates a laser beam by resonating light generated by excitation of the laser gas, the unit includes a plurality of slots formed in each of a pair of waveguides, and the pair of waveguide being arranged such that surfaces in which the plurality of slots are formed opposite to each other, and a laser tube placed between the pair of waveguides, and electromagnetic waves with in-phase electric fields are supplied to the laser tube through the plurality of slots formed in each of the pair of waveguides.
A device fabrication method according to the seventh aspect of the present invention comprises the steps of coating a substrate with a photosensitive material, exposing a pattern on the substrate coated with the photosensitive material by using any one of the exposure apparatuses described above, and developing the pattern on the exposed substrate.